A variety of surgical procedures and medical devices are currently used to relieve intraluminal constrictions caused by disease or tissue trauma. An example of one such procedure is percutaneous transluminal coronary angioplasty (PTCA). PTCA is a catheter-based technique whereby a balloon catheter is inserted into a blocked or narrowed coronary lumen of the patient. Once the balloon is positioned at the blocked lumen or target site, the balloon is inflated causing dilation of the lumen. The catheter is then removed from the target site thereby allowing blood to freely flow through the unrestricted lumen.
Although PTCA and related procedures aid in alleviating intraluminal constrictions, such constrictions or blockages reoccur in many cases. The cause of these recurring obstructions, termed restenosis, is due to the body's response to the surgical procedure and implant. As a result, the PTCA procedure may need to be repeated to repair the damaged lumen.
Stents or drug therapies, either alone or in combination with the PTCA procedure, are often used to avoid or mitigate the effects of restenosis at the surgical site. In general, stents are small, cylindrical devices whose structure serves to create or maintain an unobstructed opening within a lumen. The stents are typically made of biocompatible alloys and metals, such as stainless steel and Nitinol™, and are delivered to the target site via a catheter. Although the stents are effective in opening the stenotic lumen, the foreign material and structure of the stents themselves may exacerbate the occurrence of restenosis or thrombosis.
Drugs or similar agents that limit or dissolve plaque and clots are used to reduce, or in some cases eliminate, the incidence of restenosis and thrombosis. The term “drug(s),” as used herein, refers to all therapeutic agents, diagnostic agents/reagents and other similar chemical/biological agents, including combinations thereof, used to treat and/or diagnose restenosis, thrombosis and related conditions. Examples of various drugs or agents commonly used include heparin, hirudin, antithrombogenic agents, steroids, ibuprofen, antimicrobials, antibiotics, tissue plasma activators, monoclonal antibodies, and antifibrosis agents.
Since the drugs are applied systemically to the patient, they are absorbed not only by the tissues at the target site, but by all areas of the body. As such, one drawback associated with the systemic application of drugs is that areas of the body not needing treatment are also affected. To provide more site-specific treatment, stents can be used as a means of delivering the drugs exclusively to the target site. The drugs are stored in a tissue-compatible polymer, such as silicone, polyurethane, polyvinyl alcohol, polyethylene, polyesters, hydrogels, hyaluronate, various copolymers or blended mixtures thereof. The polymer matrix is applied to the surfaces of the stent generally during the manufacture of the stent. By positioning the stent at the target site, the drugs can be applied directly to the area of the lumen requiring therapy or diagnosis.
In addition to the benefit of site-specific treatment, drug-loaded stents also offer long-term treatment and/or diagnostic capabilities. These stents include a biodegradable or absorbable polymer suspension that is saturated with a particular drug. In use, the stent is positioned at the target site and retained at that location either for a predefined period or permanently. The polymer suspension releases the drug into the surrounding tissue at a controlled rate based upon the chemical and/or biological composition of the polymer and drug.
The above-described devices and methods for treatment of restenosis and thrombosis, and other similar conditions not specifically described, offer many advantages to potential users. However, it has been discovered that such devices and methods may be deficient in their current drug-loading and drug-delivery characteristics. In particular, the amount or volume of drug capable of being delivered to the target site may be insufficient due to the limited surface area of the stent.
In view of the above, it is apparent that there is a need to provide a fluid delivery device offering increased drug loading capabilities for stents and other prosthetic devices. It is also desirable that the drug-delivery device allows fluids to be released at variable and/or independent rates. There is also a need to provide a method of manufacturing such an improved fluid delivery device that is convenient, efficient and cost effective.